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Quick links :

Home - Part 1 - Part 2 - Part 3 - Resources

Part 3 - Connect Sensors - IoT Platform

Part 3 - Connect and test the sensors

Section 1 - Connect DHT Temperature Sensor and NeoPixel LED to Raspberry Pi

You can attach the DHT temperature and humidity sensor to any Pi that is part of the mesh network or the bridge Pi. Similarly, you can attach the RGB LED to any pi that is part of the mesh network or the bridge Pi. You can attach the DHT sensor and RGB LED to the same Pi or use different Pis.

Step 1 - Connect the DHT sensor to your Raspberry Pi

Disconnect the Raspberry Pi from the power supply before connecting the DHT sensor. Depending on the type of DHT sensor that you ordered, there are several ways to connect them.

If your DHT sensors have 4 connecting pins.follow these wiring steps. When looking at the front of the sensor (mesh case) with the pins at the bottom, the connections are (left to right):

  • +'ve voltage
  • Data
  • Not used
  • Ground

If you have a DHT mounted on a module then you need to check the pinout, usually indicated on the board, with + (to 3V pin), - (to G pin) and out or data :

DHT module

Connect the DHT-11

Connect three female to female jumper wires to the DHT-11 and then follow the Raspberry Pi pinout diagram to connect the jumpers to the Raspberry Pi:

DHT Raspberry Pi
Ground Pin 9
Data Pin 15
3.3v Power Pin 17

Step 2 - Connecting the Neopixel to the Raspberry Pi

Now you need to connect the NeoPixel to the Raspberry Pi. Before you start making any connections please disconnect the device from your power supply so there is no power getting to the device. You should never make any connection changes when the device is powered on.

Before making the connections we need to identify the 4 connecting pins coming out of the LED. If you examine the rim of the pixel cover you will see that one side is flattened (this should be the opposite side from the shortest pin) - this pin next to the flattened side is the Data Out pin. We will not be using this pin, as we only have a single pixel. You can chain pixels together connecting the Data Out pin to the Data In pin of the next pixel in the chain.

The shortest pin on the Pixel is the Data In The longest pin on the Pixel is Ground The remaining pin is +'ve voltage, which should be 5v, but it works with 3.3v that the Raspberry Pi provides.

So, with the shortest pin on the left and the flat side on the right the pinout is (left to right):

  • Data In (shortest pin)
  • +'ve Voltage
  • Gnd (longest pin)
  • Data Out (no connection)

You need to connect the Data In, +'ve voltage and ground to the Raspberry Pi as shown in the diagram. Take care to ensure that the connections are as shown, as connecting the wrong pins can damage the LED:

RaspPi LED Wiring

Step 2 - Connect the NeoPixel

Connect three female to female jumper wires to the NeoPixel and then follow the Raspberry Pi pinout diagram to connect the jumpers to :

NeoPixel Raspberry Pi
Ground Pin 6
Data Pin 12
3.3v Power Pin 1

Section 2 - Install Node-RED and Node-RED packages

Our next step will be to install packages on the Raspberry Pi(s) with the DHT sensor and RGB LED. The easiest way to connect from your laptop to each of the nodes is to complete the Bridge Access Point steps from Part 2.

Determine the IP addresses of each of the Raspberry Pi nodes in your mesh network and use ssh to connect to each of them. Install the following packages on each of the Raspberry Pi nodes that you have connected the DHT sensor and RGB LED.

Install Node.js on your Raspberry Pi

Note: The DHT sensor install does not yet work with Node.js v12

These steps detail how to install the Node-RED and node.js packages and some Node-RED prerequisites. The nodered package has a dependency on the nodejs package. The first command will also install the latest nodejs LTS package.

sudo apt-get install -y nodered
sudo npm -g install npm
sudo npm -g install node-pre-gyp
sudo npm -g install node-gyp

node-red-node-pi-neopixel Install instructions

On the Raspberry Pi with the RGB LED attached, install node-red-node-pi-neopixel prerequisites described in https://flows.nodered.org/node/node-red-node-pi-neopixel

  • Select to continue (y), but don't perform a full install (N) and don't let it configure sound (N)
curl -sS get.pimoroni.com/unicornhat | bash

don't reboot the pi just yet, so select N then install the Node-RED node for the neopixel:

sudo npm -g install node-red-node-pi-neopixel

node-red-contrib-dht-sensor DHT Sensor install instructions

On the Raspberry Pi with the DHT sensor attached, follow the BMC2835 install instructions at http://www.airspayce.com/mikem/bcm2835/index.html

wget http://www.airspayce.com/mikem/bcm2835/bcm2835-1.62.tar.gz
tar zxvf bcm2835-1.62.tar.gz
cd bcm2835-1.62
./configure
make
sudo make check
sudo make install

Finally install node-red-contrib-dht-sensor

sudo npm -g install --unsafe-perm node-red-contrib-dht-sensor

Reboot your Raspberry Pi mesh node

Reboot all the Raspberry Pis that have a DHT sensor or RGB LED sensor attached:

sudo reboot -n

Section 3 - Test the Sensors and LED

In this section, you will test the sensor readings by creating some simple Node-RED flows. Try to create the flows by following the steps. You can also import the solution flows from github.

Start Node-RED

Reconnect to each Raspberry Pi with a sensor or LED attached via ssh, login and run the following command:

node-red

Open a browser on your laptop to the IP Address or hostname.local of the desired Raspberry Pi. Node-RED is running on Port 1880 - http://pi_address:1880 or http://hostname.local:1880

Test the DHT Temperature Sensor by building this flow

Connect your browser to Node-RED running on the raspberry pi with the DHT sensor connected.

Node-RED DHT11 Test Flow

Flow Instructions

  • Select an Inject node from the left palette and drag it to your flow canvas.
  • Select a rpi-dht22 node from the palette and drag it to your flow. Double-click on the rpi-dht22 node. In the Edit dialog, select type of DHT sensor (DHT11 / DHT22) and the Pin number (15) that you have connected the female jumper wire to the Raspberry Pi (Pin 15 suggested above). Press the Done button to close the Edit dialog. DHT config
  • Select a Debug node from the palette and drag it to your flow.
  • Wire the three nodes as suggested in the screen shot.
  • Press the red Deploy button.
  • To test your flow, click on the tab leading into the Inject node.
  • Turn to the Node-RED Debug right pane by clicking on the little beetle bug icon.
  • To test your flow, click on the tab leading into the Inject node.

If you are stuck, import the solution:

  • From the Node-RED menu (☰), select Import then copy and paste the solution flow below into the Import nodes dialog

    [{"id":"2c2e21c6.64fe66","type":"rpi-dht22","z":"b701c9b1.f426a8","name":"DHT Sensor","topic":"rpi-dht22","dht":"11","pintype":"2","pin":"15","x":350,"y":180,"wires":[["78a9a66d.0663c8"]]},{"id":"6723ad1.e604c54","type":"inject","z":"b701c9b1.f426a8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":180,"y":180,"wires":[["2c2e21c6.64fe66"]]},{"id":"78a9a66d.0663c8","type":"debug","z":"b701c9b1.f426a8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":530,"y":180,"wires":[]}]

  • Press the Import button to complete the import, then click on the editor where you want to place the imported nodes

Test the NeoPixel LED by building this flow

Connect your browser to Node-RED running on the raspberry pi with the RGB LED connected.

Node-RED NeoPixel Test Flow

The NeoPixel Test flow uses Inject nodes and Change nodes to send RBG color values to the NeoPixel LED.

  • From the Node-RED menu (☰), select Import then copy and paste the solution flow below into the Import nodes dialog

    [{"id":"f0a2eeff.563c28","type":"inject","z":"7e5ededd.5355d8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":200,"wires":[["68f71092.7ed0e8"]]},{"id":"aa512d8e.317718","type":"change","z":"7e5ededd.5355d8","name":"Off - Other","rules":[{"t":"set","p":"payload","pt":"msg","to":"0,0,0","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":430,"y":320,"wires":[["17118e26.f25012"]]},{"id":"39a015f6.c6e582","type":"change","z":"7e5ededd.5355d8","name":"Pink Color","rules":[{"t":"set","p":"payload","pt":"msg","to":"#FF1493","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":430,"y":280,"wires":[["17118e26.f25012"]]},{"id":"1c861bf3.f4acf4","type":"change","z":"7e5ededd.5355d8","name":"Purple Color","rules":[{"t":"set","p":"payload","pt":"msg","to":"238,130,238","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":430,"y":240,"wires":[["17118e26.f25012"]]},{"id":"68f71092.7ed0e8","type":"change","z":"7e5ededd.5355d8","name":"Green Color","rules":[{"t":"set","p":"payload","pt":"msg","to":"#00FF00","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":430,"y":200,"wires":[["17118e26.f25012"]]},{"id":"479915c8.8880dc","type":"change","z":"7e5ededd.5355d8","name":"Blue Color","rules":[{"t":"set","p":"payload","pt":"msg","to":"blue","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":430,"y":160,"wires":[["17118e26.f25012"]]},{"id":"1624ce32.be371a","type":"change","z":"7e5ededd.5355d8","name":"Red Color","rules":[{"t":"set","p":"payload","pt":"msg","to":"red","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":420,"y":120,"wires":[["17118e26.f25012"]]},{"id":"f334b3ad.16fe7","type":"change","z":"7e5ededd.5355d8","name":"Yellow Color","rules":[{"t":"set","p":"payload","pt":"msg","to":"255,255,0","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":430,"y":80,"wires":[["17118e26.f25012"]]},{"id":"2f103b9a.c56d24","type":"inject","z":"7e5ededd.5355d8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":160,"wires":[["479915c8.8880dc"]]},{"id":"5abefa34.531984","type":"inject","z":"7e5ededd.5355d8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":120,"wires":[["1624ce32.be371a"]]},{"id":"75977be3.1cb8dc","type":"inject","z":"7e5ededd.5355d8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":80,"wires":[["f334b3ad.16fe7"]]},{"id":"b3a5588a.75cd3","type":"inject","z":"7e5ededd.5355d8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":240,"wires":[["1c861bf3.f4acf4"]]},{"id":"348d5d9c.35d402","type":"inject","z":"7e5ededd.5355d8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":280,"wires":[["39a015f6.c6e582"]]},{"id":"c52803ea.cef008","type":"inject","z":"7e5ededd.5355d8","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":320,"wires":[["aa512d8e.317718"]]},{"id":"17118e26.f25012","type":"rpi-neopixels","z":"7e5ededd.5355d8","name":"Neopixel","pixels":"1","bgnd":"","fgnd":"","wipe":"40","mode":"pcent","rgb":"grb","brightness":"100","gamma":true,"x":680,"y":200,"wires":[]}]

  • Press the Import button to complete the import, then click on the editor where you want to place the imported nodes

Test the various colours work by pressing the button on the inject nodes. Look at the change node configurations (double click on the node to open the configuration) to see the various ways you can enter colour values.

If the red and green colours are switched, then open the configuration of the Neopixel node and change the Pixel order to RGB, as some neopixels want data to be sent in order Red, Green then Blue values whilst other neopixels use a data order of Green, Red then Blue.

Quick links :

Part 3 - Connect Sensors - IoT Platform

Home - Part 1 - Part 2 - Part 3 - Resources